Nozzle plates having small, closely spaced holes are used in many industrial applications, including in printheads for ink jet printers. Typically, nozzle plates for ink jet printers are comprised of thin sheets of metal with patterns of very small, closely spaced holes. Because of the thinness of the metal sheets and the small size and close spacing of the holes, fabrication of nozzle plates is extremely difficult. Furthermore, such printheads known in the art present various problems usually manifested as poor resolution or blurry imaging.
An ink jet print head of an advanced nature and typical of current ink jet printing heads is disclosed in U.S. Pat. No. 4,555,717 to Miuro, et al. which discloses the use of pressure and potential gradients in combination with small, closely spaced holes to provide ink jet printing of a higher quality than previously known. Miura presents a laminar air flow chamber having a front channel through which a combined stream of air and ink droplets is discharged toward a writing surface. A rear channel provided through an insulative plate and axially aligned with the front channel is connected to an ink source. The laminar air flow chamber is provided with an air intake connected to a pressurized air supply directing an airstream to a point between the front and rear channels so that the air stream makes a sharp turn at the entry into the front channel resulting in a pressure gradient in the discharge path. An electric field is established by a first electrode proximate to the front channel and a second electrode on a rear side wall at the insulative plate such that, combined with the affects of the pressure gradient, the ink meniscus at the exit end of the rear channel is caused to extend toward the front channel and be torn apart into a droplet carried by the airstream and discharged through the front channel.
Various problems have been identified with respect to air pressure assisted ink jet print head mechanisms. It has been determined that a zone of stagnant air exists around the area of the drop forming orifice which allows a puddle of ink to form there. The pressure forced ink, which must break through the stagnant air, may be significantly deformed thereby, resulting in fuzzy, irregular print lines or otherwise adversely effected print quality.
Non-air assisted, as well as air assisted, ink jet printing heads have associated therewith print quality problems caused by ink wetting the drop forming orifice. Such ink wetting problems have been addressed by applying anti-wetting coatings, such as polytetrafluoroethylene, to the drop forming orifice. However, such a coating provides only a temporary solution because over time the anti-wetting coating becomes contaminated and loses its anti-wetting characteristics.
More recent studies suggest that the structure or shape of an ink jet print head drop forming orifice can significantly impact the quality of printing resulting therefrom. It has been suggested that a "mesa" structure or print head drop forming orifice which is provided in a structure of a frustoconical profile can provide drops with enhanced uniformity resulting in better quality ink jet printing.